1. Field of the Invention
Example embodiments of the invention relate to a method for calculating parameters of a thin-film transistor (TFT) and a calculating apparatus for performing the method. More particularly, example embodiments of the invention relate to a method for calculating parameters of a TFT including an amorphous semiconductor thin-film and a calculating apparatus for performing the method.
2. Discussion of the Related Art
A crystalline material, such as a metal or a semiconductor, typically has atoms that are regularly arranged to form a crystal. A crystal grain has a diameter from about 0.1 μm to over 0.1 m. In contrast, a non-crystalline or amorphous material has a solid body without a long-range regular arrangement of atoms. Compared with a crystalline material having a solid body with a 3-dimensional regular arrangement of atoms, an amorphous material has a solid body with an irregular arrangement of atoms in a long range. The amorphous material may have an arrangement of atoms similar to that of the crystalline material within a relatively short distance, but the atom arrangement of the amorphous material is disordered in a relatively long distance; therefore, the property of the amorphous material is typically not clearly defined.
For example, metal oxide glass is a typical amorphous material. The glass maintains a disordered structure at a room temperature, without being crystallized when being solidified from a liquid state. The amorphous material, which is a broad definition from the glass, is a generic term for referring to a solid body without a crystalline structure. Cooling a liquid-state metal oxide, such as silicon dioxide (SiO2) or boron trioxide (B2O3), to make a crystal is difficult, and an amorphous structure may be maintained. In contrast, the metal or the semiconductor is relatively easier to be crystallized, and forming an amorphous structure in the metal or the semiconductor using a conventional method may be difficult. A semiconductor including an amorphous material is an amorphous semiconductor.
A method for forming an amorphous semiconductor has been invented, and the material made from the method has properties different from properties of crystalline semiconductors. Amorphous silicon is a typical amorphous semiconductor. The amorphous silicon has an unclear band structure, and has a state in a band gap; therefore, the amorphous silicon as a semiconductor may be less desirable than a semiconductor with a single crystalline structure. Nevertheless, the amorphous silicon is inexpensive. A p-n junction diode or a transistor conventionally formed using a single crystalline semiconductor may be formed using a hydro-amorphous silicon that is saturated by hydrogen, given that valance electrons may be controlled. In addition, since the amorphous silicon is deposited with a relatively larger size in a relatively lower temperature, the amorphous silicon may be used as a thin-film transistor (TFT) or a visual receptor for an electro photograph; having a relatively large coefficient of light absorption, the amorphous silicon may be used as a solar cell. Recently, the amorphous silicon may be used as a component of a flexible and transparent display apparatus.
As for an amorphous metal oxide semiconductor, a lowest point of a conduction band is located at a metal cation ns orbital; therefore, the mobility of the amorphous metal oxide semiconductor almost reaches band mobility regardless of directions of the crystal, and the state-density is relatively low. Thus, the mobility of the amorphous metal oxide semiconductor is substantially better than an amorphous silicon semiconductor. Given the mobility advantage, the amorphous metal oxide semiconductor may play a significant role in next generation high performance (flexible and transparent) display apparatuses. Despite of the above-mentioned merits, changes of properties of the amorphous metal oxide semiconductor in response to electrical, optical, and thermal stresses are typically difficult to be quantifiably anticipated. To commercialize a display apparatus using an amorphous metal oxide TFT, the changes of the properties of the amorphous metal oxide semiconductor in response to electrical, optical, and thermal stresses should be defined as parameters in an actual pixel operating environment. Given the parameters, the changes of the properties may be simulated to anticipate the performance of the amorphous metal oxide semiconductor in the actual pixel operating environment.